1. Field of the Invention
The invention relates to thermoplastic resin compositions and more particularly relates to polycarbonate-silicone block copolymers and methods of their preparation.
2. Brief Description of the Prior Art
Polycarbonate-silicone copolymers have found valuable usage as coatings and adhesives for bonding laminate structures; see for example the description found in U.S. Pat. No. 4,123,588 (Molari, Jr.) issued Oct. 31, 1978. Polycarbonate-silicone copolymers are also useful as components of thermoplastic molding compositions; see U.S. Pat. No. 4,569,970 (Paul et al) issued Feb. 11, 1986.
Elastomer compositions are described in U.S. Pat. No. 4,387,193 (Giles, Jr.) which issued June 7, 1983. These elastomer compositions include polycarbonate-silicone block copolymers as a blend component. Other preparations are described in U.S. Pat. No. 3,189,662 (Vaughn) issued June, 1965.
In general, the known polycarbonate-silicone block copolymers are prepared by solution polymerization techniques. We have discovered that polycarbonate-silicone copolymers may also be prepared by melt blending a polycarbonate with a silicone bearing carboxylic acid functionality. The transesterification reaction which occurs may be carried out in conventional melt extrusion equipment, an advantage over the more complex solution polymerization technique. The resulting block copolymer exhibits unexpected physical properties, which enhance flow and thick section impact values compared to values obtained in unmodified polycarbonate. Additionally, transparency is obtained in articles molded from a blend of a polycarbonate with a functionalized silicone.